..mmm...you must have a hell of a big garden to have at least three pairs nesting there..... blue tits need quite large territories or lots of big trees in order to get adequate food for the breeding season....they aren't usually territorial but have large broods and need lots of the right kind of food for the chicks.....lets hope for some nice insect breeding weather and tons of juicy caterpillars ............I have just the one box in my small garden and the pair that have been nesting are doing just fine...good luck...........